Apparently scientists have done a test or two, and come up with the following guidelines:

Bright white should be avoided. The Whiteness of the teeth should match the whites of the eyes.

A smile’s ideal width should be no less than half the width of the face.

Both upper and lower lips should be symmetrical on each side of the mid-line of the face.

The top row of teeth should be dominant while very little should be seen on the bottom row.

All teeth on display should be straight with no visible signs of restoration work.

The teeth should diminish in size from front to back. (Those either side of the central teeth, the laterals, should be 61.8 per cent the size of the bigger teeth. The next teeth along should be 61.8 per cent of the laterals. The width of the central teeth should be 80 per cent of their height.)